Black Holes Get an Identity Check ; Scientists Now Say There's Overwhelming Evidence That They Do Exist

Article excerpt

Astronomers are scientists of faith. How else could they believe
in such an incredible thing as a black hole? It's an object that
has collapsed to such density nothing escapes its strong gravity.
Astronomers can't see it. They have no direct evidence that it
exists. Yet their faith now is so strong it's reshaping their views
of how galaxies form, how energy flows through the cosmos, perhaps
even how our universe was born.

Einstein hated the concept, even though his theory of general
relativity predicts it. Kip Thorne loves it. The California
Institute of Technology astrophysicist says "we have close to a 100
percent case that [collapsing objects] leave black holes."

Cornell University theorist Eanna Flanagan nudges even closer to
certainty, saying "I'm 100 percent convinced personally." They
expressed their confidence during a presentation organized by
Cornell's Astronomy Department in Ithaca, N.Y., last month.

Until a few years ago, even such true believers wouldn't have
been that confident. New circumstantial evidence encourages many
astronomers to consider the reality of black holes beyond
reasonable doubt.

Some of that evidence is illustrated here. A reputed black hole
at the heart of a nearby galaxy shoots a high-speed jet thousands
of light years across space. A black hole feeding hungrily in
another galaxy burps out a bubble of hot gas that is too much to
swallow. Studies of how galaxies and black holes age suggest an
intimate relationship.

To understand why such things excite astronomers requires a
nodding acquaintance with some of the mind-bending notions the
theory of space-bending black holes entails. Black holes can be as
small as several solar masses or as gigantic as the billion-solar-
mass black holes at the core of many galaxies. Massive or not,
there's no matter in the structure of a black hole. As Dr. Thorne
explains, "A black hole is made wholly and entirely solely by the
warpage of space and time."

There is no gravitational force in general relativity. The
gravity of a mass manifests itself in this warpage. Nothing escapes
a black hole because, at its perimeter, space is so strongly curved
that all paths lead into the hole. Thorne prefers to think in terms
of time. He explains that time flows inward at the edge of a black
hole. Nothing can escape because the future of everything on the
perimeter lies inside the hole.

If that sounds weird, consider what happens just outside the
perimeter. Matter under a black hole's influence orbits just as
planets orbit a star. That matter can also spiral down and be
swallowed up. But near the hole itself, it's not just matter
swirling around. A rotating black hole drags space itself around
with it, carrying along any matter in that space. Thorne describes
this as "a motion of space around a black hole in a way that's
similar to the winds around a tornado." He adds that space around a
black hole not only spins around, it slides into the black hole.
Some space slides inward at light speed as seen from the outside.

There's enormous energy involved. Thorne says the space vortex
energy represents 29 percent of the black hole's mass. He notes
that a black hole is many times more efficient at turning mass into
energy than are nuclear processes.

Not everything caught in a black-hole dance is sucked inside. The
system has to get rid of excess matter and rotational momentum.
Magnetic forces in the swirling dust and gas circling the hole
escape in powerful jets and outflowing bubbles. The interaction of
such material with itself and with interstellar or intergalactic
gas generates X-rays, gamma rays, radio waves, and sometimes
spectacular light shows.